Instead of the traditional CO2 emissions measurement, green car expert Clean Green Cars included two other major pollutants into its criteria to find the greenest manufacturer and found Fiat was top of the list.
The study included Oxides of Nitrogen (NOx) and particulates – both of which are linked to respiratory problems – as well as the CO2 emissions.
Fiat finished top with average CO2 figures of 124.6g/km, NOx of 36.4mg/km and 0.6mg/km of particulates.
Models such as the Fiat 500, which boasts emissions under 110g/km, and the 119g/km Panda have helped Fiat finish above rivals such as Toyota and Hyundai in the table.
Richard Bremner, Editor of Clean Green Cars, said: "CO2 is hugely important, but it is not the whole story. A car that is good for CO2 can be bad for other pollutants and vice versa. We have spent six months analysing data for all three pollutants to come up with the first overall pollution score."
The study found the difference in NOx and particulates between the best and worst manufacturer was much larger than CO2 emissions, indicating many manufacturers are failing to deal with other pollutants.
Jay Nagley, Publisher of Clean Green Cars, said: "Along with most of the industry, we have become increasingly irritated by "environmental scores" which purport to show manufacturers’ performance based on nothing but assumptions.
Nagley labelled the system ‘completely robust and transparent’ and claims unlike CO2 emissions tables, it does not give a ‘single magic number’.
The study used data from industry analysts and the government’s VCA database to calculate the sales-weighted performance data for each manufacturer.
Fiat’s overall position was shared with Mini, but Fiat will be buoyed by the fact many of its models are larger and use more powerful powertrains than Mini’s model range.